The present disclosure relates generally to a tissue analysis system that utilizes emission and detection of photon density waves to assess tissue characteristics, and, more particularly, to a system for evaluating scattering properties of tissue based on distribution of photons in photon density waves emitted into the tissue and features of the photon density waves detected after passing through the tissue.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Pulse oximetry may be defined as a non-invasive technique that facilitates monitoring of a patient's blood flow characteristics. For example, pulse oximetry may be used to measure blood oxygen saturation of hemoglobin in a patient's arterial blood and/or the patient's heart rate. Specifically, these blood flow characteristic measurements may be acquired using a non-invasive sensor that passes light through a portion of a patient's tissue and photo-electrically senses the light through the tissue. Typical pulse oximetry technology currently utilizes two light emitting diodes (LEDs) that emit different wavelengths of light and a single optical detector to measure the pulse rate through and oxygen saturation of a given tissue bed.
A typical signal resulting from the sensed light may be referred to as a plethysmographic waveform. It should be noted that the amount of arterial blood in the tissue is generally time varying during a cardiac cycle, which is reflected in the shape of plethysmographic waveforms. Such measurements are largely based on absorption of emitted light by specific types of blood constituents and do not specifically take scattering into account. Indeed, traditional pulse oximeters make measurements based on a manipulation of the Lambert-Beer Law, and commonly assume that the two different wavelengths of light from light emitters travel the same path length through the same tissue. Thus, scattering differences are essentially not taken into account. However, once acquired, absorption measurements, as typically acquired by traditional pulse oximeters, may be used with various algorithms to estimate a relative amount of blood constituent in the tissue. For example, such measurements may provide a ratio of oxygenated to deoxygenated hemoglobin in the volume being monitored.
The accuracy of blood flow characteristic estimation via pulse oximetry depends on a number of factors. For example, variations in light absorption characteristics can affect accuracy depending on where the sensor is located and/or the physiology of the patient being monitored. Additionally, various types of noise and interference can create inaccuracies. For example, electrical noise, physiological noise, and other interference can contribute to inaccurate blood flow characteristic estimates. Some sources of noise are consistent, predictable, and/or minimal, while some sources of noise are erratic and cause major interruptions in the accuracy of blood flow characteristic measurements. Accordingly, it is desirable to enable more accurate and/or controlled measurement of physiologic parameters by providing a system and method that takes path length and tissue scattering properties into account, and that addresses inconsistencies in physiologic characteristics of patients and issues relating to noise.